The doctrine of the four cardinal virtues has a long history, roughly paralleling that of the doctrine of the four humors. The four virtues get a significant amount of attention from Plato in Book 4 of the Republic, and also in the Symposium. Aristotle addresses them in the Nichomachean Ethics, in the context of a broader discussion of virtue (Gardiner, 1918). Other classical figures show the concept to be continually alive in Mediterranean culture (e.g. Stoics, Cicero, Porphyry) and Arabic culture (e.g Abu Hamid al-Ghazali). These virtues were thought to have a certain philosophical rigor. They were independent concepts, not derived from each other, that also did not contradict each other. Moreover, other more particular virtues could be seen to have their roots in these four (Casey, 1990).

The cardinal virtues were carried over into the European Middle ages largely due to St. Thomas Acquinas, who made an enormous effort to reconcile this pagan system with Christianity in the Summa Theologica, and succeeded in this aim. Due to that work and the work of other Scholastics, the four virtues remained part of European culture into the modern era (Pieper, 1965).
Unlike the doctrine of the four humors, the candidates for the four cardinal virtues tended to shift with time and place, resulting in several different representations of this idea, even within the works of a single author. This is an interesting phenomenon, suggesting a shifting set of hidden premises, definitions or arguments might be at play. Freezing any interpretation of the four virtues is thus problematic, but a few representations will be made for the sake of discussion.

One of Plato’s representations of the four virtues comes in his use of the city-state as a model for virtue. He came up with three classes or ‘departments’ of men, and a fourth category representing the harmonious balancing or integration of the three departments. Plato calls this concordant working of parts within a city state or an individual ‘justice’ (Cornford, 1968). Plato’s four cardinal virtues may thus be listed in PAEI order as follows:

P – Courage
A – Temperance/moderation
E – Wisdom
I – Justice

Other expressions of the four cardinal virtues involve references to justice as more of an accounting concept, or of the proper apportioning of benefits and costs to people. In this case justice move into the A-style position, moderated by mercy in the I-style position.

P – Courage
A – Justice
E – Insight/wisdom
I – Moderation/mercy

From the time of St. Thomas Acquinas to the Renaissance, prudence was taken to be one of the four virtues, and sometimes argued to be the most fundamental virtue, giving direction to the other three (Burroughs, 1955; Barnes, 1975). On this model:

P – Courage
A – Justice
E – Prudence/foresight
I – Temperance

A comprehensive account of the four virtues would require substantial historical research. Above, I simply introduce this area of inquiry, and point to its concern structure – unstable and shifting but still discernable.

6. Barnes, B. (1975). Four bookes of offices (The English Experience: Its record in early printed books published by facsimile No. 712). Norwood, New Jersey: Thetrum Orbis Terrerum, Ltd. With Walter J. Johnson, Inc.